I do not believe that your age has much to do with your desire to use drugs. Younger individuals might be more prone to drug usage but people use drugs at all ages. As you stated, much of your identity is closely tied to your professional life. You have described your professional life as currently being dissatisfying. Your desire to use drugs may be the result of your dissatisfaction with your career and, correspondingly, with other aspects of your life.
You did not detail what the problem may be. It might be a minor problem or something bigger but without more information, it is difficult to know what might be wrong.
People use drugs for various reasons but they often do it to escape reality. Being high “feels good” in the sense that they no longer have to think about or deal with their problems. Biochemically, being high is temporarily pleasurable which is another reason why people use drugs.
Using drugs is not the answer to your problem. It only has the potential to make the situation worse. My recommendation would be to discuss this fully with your therapist. If you have already done so, it might be time to think about a different therapist. Some therapists are very skilled in some areas but not in others. Perhaps your therapist has simply taken you as far as he or she can. I can’t know any of this from such a distance but I do acknowledge the possibility that change might be productive. A fresh analysis of your situation might provide insight into what may be wrong. Please take care.